In an MFP (image forming apparatus called a Multi-Functional Peripheral), a system using a thermal fusion toner as a developer to visualize an image is well known as an electrophotographic system.
In the MFP of the electrophotographic system, a latent image is visualized by a visualizing material called a toner. In the electrophotographic system, the toner is transferred to a sheet material.
The toner positioned on the sheet material remains on the sheet material by pressure and heat provided by a fuser apparatus, and a part thereof is united with the sheet material.
With respect to the fuser apparatus, a structure is widely used in which two rollers are disposed so that rotation axes of both are in parallel to each other, a specified pressure is applied between both, and specified heat is provided from at least one of the rollers. One of or both of the rollers may be substituted by an endless belt.
The toner remaining on the sheet material is melted by the heat when the sheet material moves through a fixing area between the rollers (area where both are in contact with each other in a direction orthogonal to the rotation axis), and a part thereof is united with the sheet material.
With respect to the longitudinal direction of the roller (direction in which the rotation axis extends), there is known that uneven temperature occurs dependently on the size of the sheet material (size of the image formed of the toner). From the background as stated above, there are many proposals for eliminating the uneven temperature.
For example, JP-A-2007-25280 (document 1) discloses that a heat pipe member for uniforming temperature is pressed to a pressure roller at a time of fixing operation of a small size sheet.
JP-A-2004-77683 (document 2) discloses that a heat pipe is brought into contact with the surface of a pressure roller, the heat of a roller end conducted from a heat roller is thermally transported by the heat pipe, and the temperature of the surface layer of the pressure roller is made uniform.
JP-A-2007-108690 (document 3) discloses a structure in which a roller including a heat pipe inserted in a hollow roller made of thin iron is used, and a flange part covers.
The document 1 and the document 2 merely disclose that the heat pipe contacts with the roller of a fuser apparatus from the outside and uniforms the temperature distribution. That is, it is not assumed that the heat pipe is incorporated in the inside of the roller.
Although the document 3 discloses that the heat pipe is positioned in the inside of the hollow roller, aligning (longitudinal direction) between the heat pipe and the roller is not discussed. Besides, the inclination and eccentricity of the heat pipe in the roller are not discussed.